Carcinoid tumors are malignancies originating from neuroendocrine cells, most commonly encountered in the gastrointestinal tract, in a rate of 64%, with the majority affecting the ileum. Certain genetic syndromes sometimes include carcinoid tumors in their phenotype. These malignancies may be rather asymptomatic, although occasionally they behave aggressively. They are typically diagnosed due to the effects of a locally advanced disease, or when producing symptoms because of hormone secretion (carcinoid syndrome). A better understanding of their molecular biology and behavior is demanded so that these tumors to be diagnosed precociously and managed effectively.